Electric welding system



April 6, 1943. A. L. WHITELEY ETAL ELECTRIC WELDING SYSTEM Original Filed Jan. 5, 1940 2 Sheets-Sheet 1 nventdrs: Austyn L Whiteley, Bert-ram 6 HI l "Egihs, Their Attorney.

A. L. WHITELEY s rm. ELECTRIC WELDING SYSTEM April 6, 1943.

Original Filed Jan.

5, 1940 2 Sheets-Sheet 2 TIME Fig.3.

Ir ver wtor s: Aust-yn LJWhiteIey,

s .m 0 m6 a. r t r e V. B b

Patented A r, 6, 1943 nmc'rnro WELDING srs'ruu Austyn L. Whiteley and Bertram G. Higgins, Bagby, England, as'signors to General Electric Company, a corporation of New York Original application January 5, 1940, Serial No.

312,520, now Patent No. 2,269,987, dated January 13, 1942. Divided and this application January 29, 1941, Serial No. 376,542. In Great Britain Match 20, 1939 Claims.

Our invention relates to electric translating apparatus and more particularly to electric re- I sistance welding equipment.

This application is a division of our copending patent application Serial No. 312,520, filed J anuary 5, 1940, entitled Electric valve controlv system and which is assigned to the assignee of the present application. Various features of the electric valve control system described herein are broadly claimed in the above identified application Serial No. 312,520 (now Patent No. 2,269,967,

. dated January 13, 1942).

It is an object of our invention to provide a new and improved electric resistance welding system.

It is another object a new and improved electric translating system for energizing a welding circuit and which includes apparatus for transmitting diflerent amounts of current to the weldingcircuit during predetermined intervals, and which also provides apparatus for increasing the pressure applied to the welding electrodes during a period of low current intensity which follows a period of relatively high current intensity. I

It is a further object of our invention to provide a new and improved method of electric sistance welding.

For a better understanding of our invention, reference may be had to the following description, taken in connection with the accompanyin drawings, and its scope will be pointed outin the appended claims. Fig. 1 diagrammatically illustrates an embodiment of our invention as a'pplied to a welding system for energizing an alternating current welding circuit from an, alternating current supply circuit, and Figs. 2 and 3 represent certain operating characteristics thereof.

Referring .now to Fig. 1 of the accompanyin drawings, we have diagrammatically illustrated our invention as applied to a welding system for energizing a. load circuit, such as a welding circuit, from an alternating current supply circuit alive. or immersion ignitor control members 0 lili of our invention to provide of semi-conducting material, such as boron-carhide or silicon-carbide, associated with the mercury pool cathodes. These control members re-= quire the'transmission of a current of predetermined value therethrough in order to initiate an arc discharge between the anode and the cathode. a

We provide a pair of excitation circuits 9 and I0 associated with the electric valve means 4 and 5, respectively, for transmitting unidirectional current to the control members 8 thereof to render the valves conductive and hence to effect ene'rgization'of the welding circuit I. Excitation circuits 9 and i0 include electric valves or electric discharge devices It and I2, and i2 and i4, respectively. These electric discharge devices are'also preferably of the type employing an ionizable medium and each comprises a electrical degrees with respect to the applied control grid". The excitation may be connected to responsive to the anode voltage of the associated electric valves .4 and I, respectively, and may be connected to the respective anodes through current limiting resistances i8, i1 and current protective means as fuses i9 and i9, respectively.

To render the electric discharge devices I! and I4 conductive, we provide grid circuits 2. and 2|, respectively. These grid circuits include means for impressing on the control grids l5 thereof 7 suitable biasing potentials tending to maintain the electric discharge devices nonconducting. These biasing means may comprise transformers ,22 and 23, respectively, and may be energized from any suitable source of alternating current of. proper frequency and phase displacement, preferably having a phase displacement of anode-cathode voltages of electric valves 4 and 5, respectively. The transformers 22 and 23 may be energized from the alternating current circuit 2' through suitable phase shifting apparatus (not shown). A suitable source of substantially constant negative unidirectional biasing potential .may be employed in each of the grid circuits 2.,

and 2| and may comprise a'parallel'connected capacitance 24 and a resistance ",both'of which are connected in series relation with a unidirectional conducting. device 2! and which are enersized from transformer 22 or 23. 7

Generally speaking, we provide, as explained hereinafter, new and improved electric valve tun-- ing circuits for controlling the conductivities of circuits 9 and II her of cycles of the voltage of the alternating current circuit 2 to effect energization of the welding circuit I during a corresponding interval 01' time. In addition, we provide a master timing circuit which generates a number of electrical quantities for determining independently separate or distinct intervals of conduction by the electric valve means 4 and 5 and which operate in conjunction with current or heat control apparatus to transmit diiferent amounts of current to the welding circuit I during the respective intervals. The system is capable of responding to transmit different amounts of current to the welding circuit I during contiguous intervals in response to a single circuit controlling operation.

As a means for producing a number of electrical timing quantities, we provide a master timing circuit 21. The timing circuit'Zl may :be energized from the alternating current circuit 2 through a transformer28 and a biphase rectifier 29 comprising a transformer 30, electric valves 3|, a smoothing inductance 32, and a filter circuit .33. A controlling contactor 34 may be connected in series relation with the positive terminal of the rectifier 29 and a suitable potentiometer comprising a resistance 35 may be connected across the output terminals of the rectifier 29. In order to produce a number of electrical timing quantities, we provide in parallel a pair of electric paths comprising resistances 36 and 31 and a capacitance 38, and resistances 39 and 40 and a capacitance 4|. These paths or circuits are connected to the positive terminal of the out- .put circuit of rectifier 29 and are connected to be charged from the output circuit through a suitable electric discharge device 42 preferably of the type employing an ionizable medium, such as a gas or a vapor, and having a control grid 43. Suitable initiating switches 44 and 45 are connected in series relation with the anode-cathode circuit of the electric discharge device 42 and serve to initiate the charge of the capacitances 38 and 4| from the direct current output circuit of rectifier 29, and hence initiate the generation of the electrical timing quantities. The initiating switches 44 and 45 may be arranged so that in their normal positions the capacitances 4| and 38, respectively, are short circ-uited through resistances 46 and 47, respectively which constitute discharge circuits therefor. The resistance 48 of relatively high ohmic value may be connected across the circuits including capacitances 38 and 4| to prevent the voltages of these circuits from attaining dangerously high values. A capacitance 49 is connected across the cathode and the grid of electric discharge device 42 to absorb extraneous transient voltages. In order to render the electric discharge device 42 conductive at a precise time during a cycle of voltage of circuit 2, we employ a transformer 50 preferably of the type designed to ;produce a voltage of peaked wave form and which is connected in circuit with the control grid 43. A current limiting resistance 5| may be. connected in series relation with the grid 43. Transformer 50,1f desired, may be connected to the alternating current circuit 2 through a suitable phase shifting device (not shown) This phase shifting device, of course, may be adjusted to adjust or control the time during the cycles of voltage at which the electric discharge device 42 is rendered conductive.

Switches 52 and 53 may be connected across the resistances 39 and 40, respectively, to control the time constants of the charging circuit for capacitances-38 and 4| and hence to control the duration of the electrical timing quantity. In this manner, it is possible to obtain ready control of the periods of conduction by the electric valve means 4 and 5.

To produce trains of cycles of alternating current in response to the electrical timing quantities generated by the master timing circuit 21, we provide control circuits 54 and 55 which are energized from a suitable source of alternating current correlated in phase and frequency with respect to the voltage of circuit 2. Of course, the control circuits 54 and 55 may be connected to circuit 2 by means of an insulating transformer 55 and through a control switch 56', if desired.

Control circuit 54 comprises a pair of electric discharge devices 51 and 58 preferably arranged in a leading and following relationship, respectively. The period of conductivity of the electric discharge devices 5! and 5B is determined bythe electrical timing quantity derived from the master timing means 27 through conductor 59 and a voltage divider 60 connected to the main voltage divider of the master timing means. A switch 5| may be employed to adjust or vary the interval of time during which the electric valve 5|is rendered conductive. The current limiting resistance 62 and the transient absorbing capacitance 63 may be connected in the grid circuit of the electric discharge device 51. The electric discharge device 58 is arranged to follow the discharge device 51, that is, to be rendered conductive during the following half cycle after each half cycle of conduction by the electric discharge device 51 since the devices are arranged inversely in parallel. Furthermore, the electric discharge H devices 51 and 58 are arranged to conduct current from the supplycircuit 2 through transformer 28 and through an inductance 54. Since the discharge devices 51 and 58 are arranged inversely in parallel, alternating current will be transmitted through the inductance for a number of cycles determined by the timing quantity derived from the master timing means 21. A suitable source of biasing potential, such as an alternating biasing potential preferably displaced 180 electrical degrees with respect tothe anodecathode voltage of discharge device 58, is impressed on its grid'by means of a transformer 65. A self-biasing circuit comprising a resistance 6B and a capacitance is also employed. Superimposed on the two biasing potentials there is also provided a. voltage suillcient to overcome the effect of the biasing potentials to render the discharge device 55 conductive due to the transthe terminals thereof within a reasonable range of values. In order to impress on the control grids l5 of the electric discharge devices I2 and I2 trains of half cycles or cycles of alternating voltage corresponding in length to one of the electrical timing quantities generated by circuit 21, we provide a transformer 14 energized through a resistance H and :having a pair of secondary windings 12 and 13$ Secondary winding 12 is connected to grid 15 of discharge device I 2 through resistances "and 15, and secondary winding 13 is connected to grid l5 of discharge device |3 through resistances l6 and 11.

Control circuit 55 is substantially similar to these grid circuits.

variable resistances that the left-hand terminal a the primary windcontrol circuit 84 and transmits trains of half cycles or cycles of alternating voltage corresponding to a dificrent electrical timing quantity derived from the master timing circuit 21 through a circuit including conductor 18, a voltage divider 18 and a switch 18. The control circuit 88 ining of transformer 84 is connected to the midcludes a pair of reversely connected electric valve means 88 and 8| and impresses upon a transformer 82 train-sot half cycles or cycles'of voltage to render theelectric discharge devices II and I4 conductive during a' period of time corresponding to the timing quantity derived from the master timing circuit 21. The transformer 82 comprises secondary windings 88 and 84, the former of which is connected to grid I5 of electric discharge device II through resistances 85 and 88, and the latter of which is connected to grid III of discharge device I4 through resistances 81 and 88. The control circuit 58 is connected to render discharge devices II and I4 and hence electric valves 4 and 5 conductive during a predetermined interval of time by impressing on the control grids I5 of the discharge devices a train of cycles of alternating potential to render the electric valves 4 and 5 conductive during a corresponding number of cycles. In control circuit 55 the discharge devices 88 and 81 are arranged in leading and following relationship to transmit alternating current through the inductance 88. An alternating biasing or half-oil potential may be provided by transformer 88, and a voltage for rendering the discharge device 8| conductive in response to the conduction by discharge device 88 is obtained by means of the transformer 8|. Other elements of the control circuit 88 correspond in function to that described above in connection with the control circuit 54.

In order to control the amount of current trans connection of the secondary winding of trans former 28, and that by operation of theswitch I88 there is provided means for connecting the P m voltages 180 electrical degrees displaced from each other.

Control circuit 88 is similar in all substantial respects to circuit 82. This circuit comprises a transformer I88, preferably of the type designed to produce a voltage of peaked wave form, and

comprises secondary windings I81 and I88 connected across resistances 14 and 18 in grid cir-, cuits 28 and 2 I respectively. In other words, the alternating voltages of peaked wave form generated in secondary windings I81 and I88 determine the time during the half cycles of voltage I of circuit 2 at which the electric discharge devices I2 and I8 are rendered conductive, and

' hencelcontrol the amount of current transmitted to the welding circuit I by the electric valve means 4 and 5 during one of the intervals of time established by control circuit 84 and the master timer 21. In other details, the. control circuit 88 is exactly the same as circuit 82.- Circuit includes means for controlling the phase of'lt'he voltage mitted to the welding circuit I during the inter- I vals of time established by the master timing circuit 2.1,'w'e provide control circuits 82 and 88. The control circuits 82 and 83 are sometimes referred to asheat control circuits. Circuits 82 and 88 are associated with control circuits 58 and 84, respectively, to introduce in grid circuits 28 and 2| alternating voltages of peaked wave form to determine the time during the cycles of voltage applied to electric valves 4 and 8 at which sidering control circuit 82in particular, this circuit comprises a suitable means such as a saturable inductive transformer '84 having a primary winding 85 and a pair of secondary windings 88 and 81. A suitable capacitance may be con nected across the primary winding 88 of the the electric valves are rendered conductive. Conphase of the alternating voltage of peaked wave form generated in windings'88 and 81, we provid suitable phase shifting circuits preferably of the static impedance type and which may comprise a capacitance 88, an inductance I88, a resistance IIII, and switches I82 and I88. Other suitable ployed position of the generated in windings 88 I84 andI88 may also'be' emimpressed on the primary winding of transformer I88 and hence controls the phase of the alternating voltages of peaked wave form induced I in secondary windings I 81 and I88.

In many electric welding applications, it is desirable to control the pressure exerted by the electrodes at a definite time during the welding operation. We employ a circuit I 88 for operating a control circuit 8' which, in turn, controls apvparatus for varying the pressure exerted by the welding electrodes.v

a transformer III, a suitable rectifying'device H2 and a. filtericircuit H8 comprising capacitances H4 and an inductance II8. A suitable voltage divider,including'resistances H8 and H1 may be connected across the direct current terminals H8 and- H8. In order to effect energization of the con-trol circuit I III at the desired time during the welding cycle and hence to increase the pressure between the welding electrodes at the desired time, we provide in circuit I88 an electric discharge devicej28 for energizing theactuatingcoil I2I,of a relay I22.- The. electric discharge device I28 is preferably of the gaseous type having its anode-cathodecircuit connected in series relation with the actuating coil'I2I of relay J22. A capacitance I28 and a resistance I24 may be connected. across the actuating'coil I in order to transmit a substantially unidirectional current through-the actuating coil I 2I during -the interval of energization thereof. The

actuating coil I2I is connected to be energized from the alternating current circuit 2 through transformer 28 and a current/limiting, resist.-'

ance I28. i

The timing of the relay I22 is effectedby means of a capacitance I28 which is connected in series relation with the grid I21 of discharge device I28. Normally, the discharge device IN is maintained nonconductive by virtue of the connection of the grid I21 to a point more negative in potential than its cathode. obtained by connecting the grid I21, to a rela tively negative point in a voltage divider. I28 through a resistance I28. A timing switch I88 may also be connected in series relation with the grid I21 and the'voltage divider I28 in order to initiate the operation. A discharge resistance III winding 88 selectively to alternating The circuit I88 comprises If desired,-this effect may be is connected across the terminals of the capacitance I26 to reset the circuit.

The circuit II may be connected to suitable means for increasing the pressure exerted by the welding electrodes on the Work. As a diagrammatic illustration of such apparatus, we have chosen to show a coil I32 which is connected to be energized from a suitable source of current such as a battery I33 to increase the pressure exerted by the electrodes on the work at a definite time during the welding cycle. For example, the switch I may be arranged to be operatedsimultaneously with switches 44 and to initiate the operation of circuit I09 simultaneously with the initiation of the operation of the timing circuit 21. The potentiometer I28 may be adjusted so that the pressure is increased at the beginning of the second period of energization of the welding circuit I, that is at the beginning of the period of lower current intensity. It will be understood that the means shown for increasing the pressure is merely a diagrammatical illustration.

The operation of the embodiment of our invention shown in Fig. 1 will be explained by considering the system when it is operating to transmit alternating current to the welding circuit I during predetermined intervals of time. and in which the values of the current transmitted to the welding circuit I are different throughout the respective intervals of energization thereof. As will be well understood by'those skilled in the art, the magnitude of the current transmitted to the welding circuit I will be increased in value as the time of initiation of arc discharges in the electric valve means 4 and Ii is advanced from a lagging position to a position more nearly in phase with the zero value at the beginning of the positive half cycles of anode-cathode voltage. Conversely. as the time of initiation of the arc discharges is retarded, the magnitude of the current transmitted to the welding circuit I is decreased in value.

The master timing circuit 21 generates two electrical timing quantities of different duration to control circuits 54 and and thereby produces two different trains of cycles of control voltage or current of diiferent duration. The "manner in which the timing circuit 21 generates these electrical timing quantities will now be explained. With the control switches 44 and 45 in the positions shown, the capaci ances 38 and 4| are short circuited and when the switches 44 and 45 are moved to the left-hand position the electric discharge device 42 will be connected in circuit with the capacitances 38 and. to initiate the charging of these capacitances from the output circuit of rectifier 29. The exact time at which the charging of capacitances 38 and 4| is initiated is determined by the setting of the peak voltage introduced in the grid circuit of discharge device 42 by means of the transformer 50. The time constants of the charging circuits for capacitances 3| and 4|, in conjunction with voltage dividers l0 and 1!, determine the duration of the timing quantities generated by circuit 21. In order to obtain timing quantities of diiferent duration, the resistances I8 and 31, and. 39 and 40 are adjusted to have different values.

' The operation of the master timing circuit 21 may be explained more fully by referring to the operating "characteristics shown in Fig. 2. The effect of the adjustment of the voltage dividers which the electric discharge devices 51 and II,-

and 40 and ll in circuits 54 and 55 respectively, are rendered conductive. Curves N and M show the relation between the time required to render discharge devices 51 and 58 non-conductive and the setting of the voltage divider 60. Curve M shows the reationship existing when the switch BI is in the position indicated in Fig; 1, while 7 curve N shows the relationship existing when the switch BI is moved to the left-hand position. With a certain setting of the slider or contact of voltage divider N, the duration of the final portion of the welding period may be adjusted to the horizontal line 0, while on moving the contact downwardly the duration of the welding period may be reduced to the time indicated by the horizontal line P. On changing the switch BI to the second position, that is to the lefthand position, it is obvious that the two time periods may. by equivalent settings of the controls, be considerably increased since the lines o and P will be extended 'to cut curve N.

The control circuits 84 and i5 transmit to the primary windings of transformers 1! and 82, respectively, trains of cycles of alternating voltage, the duration of the trains and the number 0! cycles in the respective trains being different because of the difference in length of the electrical timing quantities derived from circuit 21.

60 and "determines the period of time during 75.

Electric discharge devices 51. 58 and 40, II are rendered conductive by the transmission of current through resistances 38, 31 and 39, 44, respectively, upon the charging of capacitances II and H through the electric discharge device 42. During the charging of the capacitances 24 and M the common junctures of the resistances and the associated capacitances are. lowered to eifect a corresponding lowering in potential of the cathodes of electric discharge devices 51 and III and thereby render these discharge devices conductive by establishing a sumcient potential difference between the respective control grids and the associated cathodes. The electric discharge devices 51 and SI, and III and II in circuits 64 and 55, respectively, conduct current alternately to transmit these cycles of alternating current to transformers 10 and 02.

The electric valves 4 and 5 normally are nonconductive and are rendered conductive by the transmission of current to the immersion-ignitor control members 8. The electric valve 4, for example, is rendered conductive when either electric discharge devlce'II or I2 is rendered conductive, and likewise the electric valve 5 is tendered conductive when either electric discharge device I3 or I4 is rendered conductive. To explain the operation of the system, it will be assumed that the control circuit 55 transmits a smaller number of cycles of alternating current to the transformer 82 than the number of cycles transmitted to transformer III by circuit 54. Furthermore, it will be assumed that control circuit 92 is adjusted so that the alternating voltages of peaked wave form which determine the time at which the electric discharge devices II and I4 are rendered conductive is advanced substantially with respect to the voltages of peaked wave form produced by secondary-windings I 01 and I08 which determine the time at which discharge devices I2 and I3 arerendered conductive. In

other words. during the first interval of conduc tion by electric valves 4 and I, the length of the period of energization of thewelding circuit I is determined by the control circuit 55 through discharge devices II and I4. and the length of of-current will be transmitted to cult I. Of course, when circuit i4takes over ductive at the desired circuit I is determined by the control circuit 54 acting upon valves I2 and I 3. It will be understood that during the first interval of energization of the welding circuit I, both control circuits I4 2I, in conjunction with the rectiilers 26, produce a substantially unidirectional bias. The presence and 55 tend to render the eletric valves 4 and 5 conductive, but circuit 54' is ineffective due to the adjusted to produce a peak voltage lagging the peak voltage of circuit 92. In other words, the first discharge device of discharge devices II, l2 and I3, I4 to be rendered conductive effects initiation or an arc discharge in the associated principal electric valves 4 and 5, respectively, and immediately upon such action the anode-cathode voltage decays to a value substantially equal to the arc drop or the valve and the second discharge device to be rendered conductive is ineffective. transmitted by circuit 554 exceed those transmitted by circuit 55, circuit 54 and circuit 93 assurne control during an interval of' time equal to the diilerence in length of the two electrical timing quantities derived from circuit 21. After the expiration of the timing quantity derived from voltage divider I9, control circuit 55 becomes inoperative and control circuit 54 takes over the control of the system. At that time, due to the fact that circuit 99 is adjustedto produce peak voltages retarded in phase with respect to those previously produced by circuit 92, a reduced value the welding circontrol, electric valves 4 and 5 are rendered conductive by means of electric discharge devices I2 and .n.

The mannerin which the grid circuits 2!! and 2| control electric valves 4 and i 'to'transmit ditierentamounts'ot current to the welding circuit 1 during predetermined different intervals may be more fully explained by considering the oper-' ating characteristics shown inFig. .3. Curve A 0! Fig. 3 represents one-halicycle oi. anode voltage applied to one 0! the control valves, such as electric discharge device I2. Curve B shows the charge device; and curve C represents theblockmeans of transformer 22. Superimposed on the biasing potential is the releasing or iiringpoteniactthat its associated heat control circuit 93 is However, since the trains of impulses corresponding critical grid voltage for that dising or biasing potential impressed thereon by tial represented by curve D which is derived from circuit 54 through secondary winding l2 of transformer 10. Curve Erepresents the resultant of the two curves 0 and D on which is superimposed the peaked voltage derived from secondary winding III of transformer I08 in circuit 93. It .is evident that the amplitude of the voltage of peaked wave form must be such that it is capable of diminishing the the discharge device cal voltage to enable the valve to become coninstant, and it must therefore have an amplitude atleast equal to the maximum difference between the curves Band E. With such an amplitude, however, it the peak voltage is advanced to a position indicated in the dotted line 'at- G to give a large average current flow through the valve, the .peak voltage will be able, even in the absence oi the'releasing voltresistance "inserted in the grid circuits 29 and negative bias on the grid of I2 to a value above the criti-- electrodes and means for of the unidirectional bias increases the precision of control" It will be understoodthat the magnitude o'i'the currenttransmitted to the load circult during the various intervals of energization may be adjusted or controlled bymeans oi the switch m may be operated simultaneously with switches 44 and 45 so that the relay I22 is operated at the beginning of the second period of energizaticn oi the welding circuit I. The relay I22 is operated to close its contacts to effect enerigzation of thecoil I32 at the beginning of the second or low current intensity interval of energlzation. Of course, the circuit. I09 may be adjusted by means of the voltage divider I28 to determine the time during the welding cycle at which this increased pressure is applied.

While we have shown and described our invention as applied to particular systems of connections and as embodying various devices diagrammatically shown,.it will be obvious to those skilled in the art that changes and modifications may be made without departing from our invention, andwe, therefore, aim in the appended claims to' cover all such changes and modification 'as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination, an alternating current supply circuit, a welding circuit including welding controlling the pressure exerted by said electrodes upon the work, electric translating apparatus connected between said circuits, excitation means for controlling said translating apparatus to transmit to said .welding circuit a predetermined value of current.

' during a predetermined number of cycles of voltage or said alternating current supply circuit and for transmitting to said welding circuit a predetermined smaller value of current during an interval of time subsequent to said first mentioned,- interval, and timing means energized from said:

supply circuit for controlling thepressure controlling means to increase by said electrodes during the second mentioned interval and for controlling said excitation means to establish the above stated current-time relationship.

'2. In combination, an alternating current supply circuit, a welding circuit including welding electrodes and means for controlling the pressure exerted by said electrodes upon the work,

electric translating apparatus connected between I said circuits for 'efiecting energization of the welding circuit, excitation means for controlling said translating apparatus to transmit to said a welding circuit a predetermined value of current during a predetermined number of cycles of voltage of said alternating current supply circult and for transmitting to said welding'circuit a predetermined diflerent smaller value of current during a second intervalfioiji'time subsequent to said first mentioned interval,=and timing means for controlling the pressure controlling means, to vary the pressure exerted by said electrodes during said intervals'andfor controlling said excitation means to establish the above stated curreiit-timerelationship.

the pressure exerted 3. In combination, an alternating current supply circuit, a load circuit including welding electrodes, pressure means for controlling the pressure exerted by said electrodes upon the work, electric translating apparatus connected between said supply circuit and said welding circuit and comprising electric valve means having a control member, means connected to said control member for controlling said electric valve means to transmit to said welding circuit current of a predetermined value during a predetermined number of half cycles of voltage of saidsupply circult and for transmitting to said welding circuit a second predetermined smaller value oi current during an interval of time subsequent to the first mentioned interval, and timing means energized from said supply circuit for controlling the pressure controlling means and for increasing the pressure exerted by said electrodes during the second mentioned interval.

4. In combination, an alternating current supply circuit, a welding circuit including welding electrodes, means for controlling the pressure exerted by said electrodesuponthe work, electric translating apparatus connected between said supply circuit and said welding circuit and comprising a pair of reversely connected electric valve means each provided with a control member. excitation means connected to the control members for controlling the conductivity of said electric valve means and for controlling said electric valve means to transmit to said welding circuit a predetermined value 01 current during a. predetermined number 0,! half cycles of voltage of said supply circuit and for transmitting to said welding circuit a predetermined lower value of current during the interval of time subsequent to the first mentioned interval, and timing means for controlling the pressure controlling means and for increasing the pressure exerted by said electrodes during the second mentioned interval and for controlling said excitation means to establish the above stated current-time relationship.

5. In combination, an alternating current supply circuit, a welding circuit including welding electrodes, means for controlling the pressure exerted by said electrodes upon the work electric translating apparatus connected between said'supply circuit and said welding circuit and comprising a pair of reversely connected electric valve means each provided with a control member, excitation means connected to the control members for controlling the conductivity of said electric valve means and for transmitting to said welding circuit a predetermined value oi current during a predetermined number oi halt cycles of voltage of said supply circuit and for transmitting to said welding circuit a predetermined lower value of current during the interval of time subsequent to the first mentioned interval, and electric valve timing means energized from said supply circuit for controlling the pressure controlling means and for increasing the pressure exerted by said electrodes during the second mentioned interval and for controlling said excitation means to establish the abovestated current-time relationship.

AUSTYN L. WHITEIEY. 'BERTRAM G. HIGGINS. 

